LONDON
— Northern Ireland's most hardened terrorists now face the prospect of near-total isolation.

They are also having to contend with the toughest antiterrorist laws ever devised by the British and Irish governments.

As President Clinton arrived in Belfast yesterday, the parliaments in London and Dublin were putting the finishing touches to new measures designed to help track down and severely punish members of renegade terrorist groups.

The prime target of the urgently framed legislation is the self-styled Real IRA, the breakaway republican group responsible for last month's bombing in the town of Omagh that killed 28 people and injured 220.

The new laws will make it possible to arraign, though not convict, suspected terrorists on the word of a senior police officer, and enable security forces to seize the money and property of known terrorists. In the future, when terrorist suspects refuse to answer questions, their silence can be used as evidence against them.

At the same time, signs are multiplying that once bitterly opposed Protestant and Catholic groups are building bridges and are trying to accelerate the peace process by marginalizing those hostile to it.

On Tuesday, Sinn Fein president Gerry Adams, whose party is considered the political arm of the Irish Republican Army, announced that violence was "a thing of the past."

On Wednesday, Martin McGuinness, Mr. Adams's chief lieutenant, said he was prepared to work constructively with Canadian Gen. John de Chastelein, head of the international body charged with overseeing the turning in of terrorist arms.

Yesterday it was widely reported that Ulster Unionist leader David Trimble, chief minister in the Northern Ireland assembly, would hold a first-ever meeting next Monday with Adams. Hitherto Mr. Trimble has refused direct talks with Sinn Fein, but McGuinness's involvement in weapons decommissioning appears to have softened his attitude.

Belfast-based political analyst Paul Bew says Trimble plans to "open a dialogue" with Adams Monday, ahead of the first meeting a week later of the Northern Ireland assembly. He says the dialogue could set the scene for Trimble agreeing to Adams joining Northern Ireland's fledgling government, despite reservations on the part of many Unionists.

British government sources said yesterday that some convicted terrorists held in Belfast's top security Maze prison were likely to be released next week under the terms of the April peace agreement.

THE urgency with which the British and Irish governments have passed the new antiterrorist measures has stirred opposition from civil rights groups and left-wing politicians.

In London and Dublin the legislation was pushed through all its stages in two days. In the House of Commons, in an emergency session, 19 members of Mr. Blair's own Labour Party voted against the measures. Tony Benn, a former Cabinet minister and left-wing member of the Labour Party, said Parliament was being used "as a rubber stamp" by a government "acting like the Kremlin under the Communists."

Defending the measures, Blair said they were a "proportionate and targeted response to deal with small and evil groups of violent men who seek to wreck the hopes of peace." He announced his intention to implement "long-held plans to make it a criminal offense of conspiracy to commit offenses outside the United Kingdom."

Ahead of votes in the Commons, Blair softened the antiterrorist measures by agreeing to allow suspects access to legal counsel. Also, to secure a conviction, the word of a police officer will have to be corroborated by other evidence. Earlier drafts of the antiterrorist bill did not require corroboration.

Britain's antiterrorist package remains Draconian, however, and it closely matches laws passed yesterday by both houses of the Dail (parliament) in Dublin.

In a tough speech to the Dail Wednesday, Irish Minister Bertie Ahern said: "The Real IRA cannot hope to take on the people of Ireland and win. They have a stark choice. They can heed the will of the Irish people, or they can defy us to put them out of business."

The lower house of the Dail passed the antiterrorist measures without a vote.

As in London, the overriding theme of Irish government statements is that, after the Omagh bombing and the widespread public revulsion it evoked, the Real IRA and other dissident groups can expect no mercy from the security authorities.

Other splinter groups opposed to the peace process include the self-styled "continuity" IRA. The total membership of such organizations is thought to be under 200. But, as Omagh proved, they have access to explosives and the will to use them.

Soon after Mr. Clinton arrived in Belfast yesterday, Blair joined him. The two leaders then traveled to Omagh to inspect bomb damage and meet relatives of those who died in the blast. Clinton's itinerary was then to include a visit to Dublin.

Clinton told a gathering of 2,000 people at Belfast's Waterfront Hall: "As you work to change the shape and future of Northern Ireland, you can count on America." But he said the future is "up to you."

"Difficult, sometimes wrenching decisions lie ahead but they must be made," Clinton said. he urging people to "rise above feuds, not fuel them."